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Pnmhistmap User Manual(0)						Pnmhistmap User Manual(0)

NAME
       pnmhistmap - draw a histogram for a PGM or PPM file

SYNOPSIS
       pnmhistmap

       [-red] [-green] [-blue]

       [-black] [-white]

       [-max N]

       [-lval] [-rval]

       [-height] [-width]

       [-dots]

       [-verbose]

       [pnmfile]

       Minimum	unique	abbreviation of option is acceptable.  You may use double hyphens instead
       of single hyphen to denote options.  You may use white space in place of the  equals  sign
       to separate an option name from its value.

DESCRIPTION
       This program is part of Netpbm(1)

       pnmhistmap  reads  a  PNM  image as input and produces an image showing a histogram of the
       color (or gray) values in the input.  A PGM input results in a PBM output.   A  PPM  input
       results	in  a  PPM  output with three overlaid histograms: a red one for the red input, a
       green one for the green input, and a blue one for the blue input.

       For example, from the following image produces the following histogram:

       image histogram from image

       If the input is PBM, pnmhistmap produces an error message and no output image.

OPTIONS
       -red

       -green

       -blue  Include the indicated color component in the output.  If you specify none of these,
	      pnmhistmap include all three.

	      These options are meaningless if the input is PGM.

	      These  options  were  new  in Netpbm 10.26 (January 2005).  Before that, pnmhistmap
	      always included all three color components.

       -dots  Plot the histogram as dots.  By default, pnmhistmap plots bars.

	      Example of dots:.B -dots example

	      This option was new in Netpbm 10.26 (January 2005).  Before that, pnmhistmap always
	      plotted bars.

       -lval minpixval

       -rval maxpixval
	      These options specify the range of intensity values to include.  pnmhistmap ignores
	      intensities less than minpixval and greater than maxpixval.  So the  left  side  of
	      the histogram corresponds to minpixval and the right side corresponds to maxpixval.

	      By default, pnmhistmap plots the entire possible range: zero to the maxval.

	      These  options  were  new  in Netpbm 10.26 (January 2005).  Before that, pnmhistmap
	      always plotted from zero to the maxval.

       -height

       -width These options specify the dimensions, in pixels of the histogram image.

	      The default height is 200 pixels.

	      The default width is one pixel for each plotted intensity value (so it's controlled
	      by  the  maxval of the image and the -lval and -rval options).  The 'count buckets'
	      in the histogram are always one pixel wide.  If you specify a width less	than  the
	      number  of  plotted  intensity  values, a bucket represents more than one intensity
	      value.  If you specify a width greater that the number of plotted intensity values,
	      some buckets represent no color (the count is zero).

	      This  option  was  new in Netpbm 10.26 (January 2005).  Before that, the dimensions
	      were always what the default is today.

       -black Ignore the count of black pixels when scaling the histogram.

       -white Ignore the count of white pixels when scaling the histogram.

	      The -black and -white options, which can be used separately or together, are useful
	      for  images with a large percentage of pixels whose value is zero or 255, which can
	      cause the remaining histogram data to become  unreadably	small.	 Note  that,  for
	      color  inputs,  these options apply to all colors; if, for example, the input has a
	      large number of bright-red areas, you will probably want to use the -white option.

       -max N Force the scaling of the histogram to use N as the largest-count	value.	 This  is
	      useful  for  inputs  with  a  large percentage of single-color pixels which are not
	      black or white.

       -verbose
	      Report the progress of making the histogram, including the largest-count value used
	      to scale the output.

LIMITATIONS
       pnmhistmap  assumes  maxval is always 255.  Images with a smaller maxval will only use the
       lower-value side of the histogram.  You can overcome  this  either  by  piping  the  input
       through pamdepth or by cutting and scaling the lower-value side of the histogram.  Neither
       is a particularly elegant solution to the problem.

SEE ALSO
       pgmhist(1) , ppmhist(1) , pgm(1) , ppm(1)

AUTHOR
       Wilson H. Bent. Jr. (whb@usc.edu).

netpbm documentation			   13 July 2009 		Pnmhistmap User Manual(0)
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